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  <div class="section" id="module-pydoc">
<span id="pydoc-documentation-generator-and-online-help-system"></span><h1>26.2. <a class="reference internal" href="#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal"><span class="pre">pydoc</span></code></a> — Documentation generator and online help system<a class="headerlink" href="#module-pydoc" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/pydoc.py">Lib/pydoc.py</a></p>
<hr class="docutils" id="index-0" />
<p>The <a class="reference internal" href="#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal"><span class="pre">pydoc</span></code></a> module automatically generates documentation from Python
modules.  The documentation can be presented as pages of text on the console,
served to a Web browser, or saved to HTML files.</p>
<p>For modules, classes, functions and methods, the displayed documentation is
derived from the docstring (i.e. the <code class="xref py py-attr docutils literal"><span class="pre">__doc__</span></code> attribute) of the object,
and recursively of its documentable members.  If there is no docstring,
<a class="reference internal" href="#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal"><span class="pre">pydoc</span></code></a> tries to obtain a description from the block of comment lines just
above the definition of the class, function or method in the source file, or at
the top of the module (see <a class="reference internal" href="inspect.html#inspect.getcomments" title="inspect.getcomments"><code class="xref py py-func docutils literal"><span class="pre">inspect.getcomments()</span></code></a>).</p>
<p>The built-in function <a class="reference internal" href="functions.html#help" title="help"><code class="xref py py-func docutils literal"><span class="pre">help()</span></code></a> invokes the online help system in the
interactive interpreter, which uses <a class="reference internal" href="#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal"><span class="pre">pydoc</span></code></a> to generate its documentation
as text on the console.  The same text documentation can also be viewed from
outside the Python interpreter by running <strong class="program">pydoc</strong> as a script at the
operating system’s command prompt. For example, running</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="n">pydoc</span> <span class="n">sys</span>
</pre></div>
</div>
<p>at a shell prompt will display documentation on the <a class="reference internal" href="sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal"><span class="pre">sys</span></code></a> module, in a
style similar to the manual pages shown by the Unix <strong class="program">man</strong> command.  The
argument to <strong class="program">pydoc</strong> can be the name of a function, module, or package,
or a dotted reference to a class, method, or function within a module or module
in a package.  If the argument to <strong class="program">pydoc</strong> looks like a path (that is,
it contains the path separator for your operating system, such as a slash in
Unix), and refers to an existing Python source file, then documentation is
produced for that file.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">In order to find objects and their documentation, <a class="reference internal" href="#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal"><span class="pre">pydoc</span></code></a> imports the
module(s) to be documented.  Therefore, any code on module level will be
executed on that occasion.  Use an <code class="docutils literal"><span class="pre">if</span> <span class="pre">__name__</span> <span class="pre">==</span> <span class="pre">'__main__':</span></code> guard to
only execute code when a file is invoked as a script and not just imported.</p>
</div>
<p>When printing output to the console, <strong class="program">pydoc</strong> attempts to paginate the
output for easier reading.  If the <span class="target" id="index-1"></span><code class="xref std std-envvar docutils literal"><span class="pre">PAGER</span></code> environment variable is set,
<strong class="program">pydoc</strong> will use its value as a pagination program.</p>
<p>Specifying a <code class="docutils literal"><span class="pre">-w</span></code> flag before the argument will cause HTML documentation
to be written out to a file in the current directory, instead of displaying text
on the console.</p>
<p>Specifying a <code class="docutils literal"><span class="pre">-k</span></code> flag before the argument will search the synopsis
lines of all available modules for the keyword given as the argument, again in a
manner similar to the Unix <strong class="program">man</strong> command.  The synopsis line of a
module is the first line of its documentation string.</p>
<p>You can also use <strong class="program">pydoc</strong> to start an HTTP server on the local machine
that will serve documentation to visiting Web browsers.  <strong class="program">pydoc -p 1234</strong>
will start a HTTP server on port 1234, allowing you to browse the
documentation at <code class="docutils literal"><span class="pre">http://localhost:1234/</span></code> in your preferred Web browser.
Specifying <code class="docutils literal"><span class="pre">0</span></code> as the port number will select an arbitrary unused port.</p>
<p><strong class="program">pydoc -b</strong> will start the server and additionally open a web
browser to a module index page.  Each served page has a navigation bar at the
top where you can <em>Get</em> help on an individual item, <em>Search</em> all modules with a
keyword in their synopsis line, and go to the <em>Module index</em>, <em>Topics</em> and
<em>Keywords</em> pages.</p>
<p>When <strong class="program">pydoc</strong> generates documentation, it uses the current environment
and path to locate modules.  Thus, invoking <strong class="program">pydoc spam</strong>
documents precisely the version of the module you would get if you started the
Python interpreter and typed <code class="docutils literal"><span class="pre">import</span> <span class="pre">spam</span></code>.</p>
<p>Module docs for core modules are assumed to reside in
<code class="docutils literal"><span class="pre">https://docs.python.org/X.Y/library/</span></code> where <code class="docutils literal"><span class="pre">X</span></code> and <code class="docutils literal"><span class="pre">Y</span></code> are the
major and minor version numbers of the Python interpreter.  This can
be overridden by setting the <span class="target" id="index-2"></span><code class="xref std std-envvar docutils literal"><span class="pre">PYTHONDOCS</span></code> environment variable
to a different URL or to a local directory containing the Library
Reference Manual pages.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span>Added the <code class="docutils literal"><span class="pre">-b</span></code> option.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span>The <code class="docutils literal"><span class="pre">-g</span></code> command line option was removed.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.4: </span><a class="reference internal" href="#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal"><span class="pre">pydoc</span></code></a> now uses <a class="reference internal" href="inspect.html#inspect.signature" title="inspect.signature"><code class="xref py py-func docutils literal"><span class="pre">inspect.signature()</span></code></a> rather than
<a class="reference internal" href="inspect.html#inspect.getfullargspec" title="inspect.getfullargspec"><code class="xref py py-func docutils literal"><span class="pre">inspect.getfullargspec()</span></code></a> to extract signature information from
callables.</p>
</div>
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